The chemical or physical processes of teeth restoration in general as well as adhesive compositions for the dental art in particular, are still under investigation and therefore the technology tends to be experimental and only partially theoretical.
The strength of a joint bonded by an adhesive depends on adhesion of a composition to the surfaces joined as well as to the cohesion within the adhesive itself. The respective adhesive must cover the surfaces thoroughly and form a continuous bond line.
Conventional adhesive compositions used for dental purposes, are generally based on acrylic resins, such as acrylic or methacrylic, which in the presence of a free-radical initiator are mainly used as curable compositions for this purpose. Typical examples of such resins are based on methyl methacrylate, 2,2-bis(p-2'-hydroxy-3-methacryloxypropoxyphenyl)propane, etc.
According to Japanese Patent Number 72'19409, it is suggested to use (methacryloxy)ethyl trimellitate-ethylene glycol monomethacrylate polymer as an adhesive possessing a heat resistant anaerobic property, using benzoquinone as an inhibitor.
A successful dental composition, which is now widely used is 4-methacryloxy-methyltrimellitic anhydride known also under the name of 4-META. Thus, according to the U.S. Pat. No. 4,148,988, the dental adhesive composition is based on the following constituents:
(1) 4-META; (2) at least one ethylenically unsaturated monomer, other than 4-META, which is copolymerizable with 4-META, and (3) at least one catalyst selected from initiators and photosensitizers. It is claimed that these compositions possess a strong adhesiveness to either enamel or dentin of teeth, the resulting bonded structure being prominently excellent in its properties, such as water resistance and durability, without requiring any prior treatment. Nothing is mentioned in the patent in respect to tooth restoration.
There are many papers which deal with the physical properties of resins and cements based on 4-META. In a paper by Suzuky et al (Journal of Biomedical Materials Research 24, Aug. 8, 1990, 1091-1103) it is reported on the adhesive bonding of composite resins to dentin.
In another paper by Ishihara et al (Journal of Biomedical Materials Research, Vol. 23, No. 12, Dec. 12, 1989, 1475-1487) a new bone cement is described. It consists of 4-META and methyl methacrylate as monomers and tri-n-butyl borane as an initiator. It is mentioned that the tensile bond strength between bone and metals adhered with the cement was above 7 MPa.
According to the PCT patent application No. 85/00514, an improved method and compositions are described for the adhesion of composites to dentin, enamel and other substrates. According to the method, the substrate is first treated with an aqueous solution which comprises: at least one acidic salt of a polyvalent cation, such as titanium, vanadium, nickel, iron, copper, which can bind to dentin or enamel surface sites, at least one anion which forms a relatively water-insoluble precipitate with calcium and at least one carboxyl group. The resultant surface is further treated with a solvent containing a composition which comprises N-phenylglycine and finally treated with a solution which contains an additional compound, among others 4-META being mentioned: It is claimed that the method imparts an improved treatment of cervical erosions, root caries and other dental conditions, thus eliminating much mechanical cutting of dentin, required for retention of restorations.
It appears that all the above mentioned adhesive compositions are useful to bind dentine to a restorative material. However, the above conventional compositions do not possess sufficient bonding force to bind composite resin on top of an amalgam in restoration. Furthermore, in the use of amalgam which is commonly used in the restoration practice together with a known adhesive composition, the strength developed is poor. This might be one of the reasons why no methods are known on their use as an adhesive reagent to bind and cover amalgam restoration.
It is an object of the present invention to provide new dental compositions useful in the process of restoring teeth. It is another object of the present invention to provide new dental compositions useful for the restoration of teeth, which possess a strong adhesiveness to "fresh" (i.e. just prepared) and "old" amalgam as well as to dentin. It is a further object of the present invention to provide new dental adhesive compositions useful for the restoration of teeth, which possess a water resistance and durability. It is yet another object of the present invention to provide new dental polymeric compositions, useful for the restoration of teeth, which are polymerized in-situ.